Qualities That Contribute

Many of the best streets have trees, but not all of them. Many but not all of the best streets have special public places to sit or stop along the way. Gateways, fountains, obelisks, and streetlights are among the physical, designable characteristics on great streets, but not always. Some physical qualities, then, contribute mightily to making great streets but are not required. On particular streets they can be compelling and interesting as the necessary qualities, or they can add the salt an pepper, the spice or difference that turns a good street into a great one. Some factors, like accessibility and topography, are ever present. Other variables, most notably density and land issues, though not directly part of street design, are so intimately related to physical place that they cry out for discussion.

Trees

Given a limited budget, the most effective expenditure of funds to improve street would be probably on trees. Assuming trees appropriate in the first place (not on Stroget, for example) and that someone will take care of them, trees can transform a street more easily than any other physical improvement. Moreover, for many people trees are the most important single characteristic of a good street.

Trees can do many things for a street and city, not the least of which is the provision of oxygen, and of shade for comfort. Green is a psychologically restful, agreeable color. Trees move and modulate the light. In terms of helping streets to work functionally, when planted in lines along a curb or even in the the cartway they can effectively separate pedestrians from machines, machines from machines, and people from people. The trunks and branches create a screen, sometimes like a row of columns that gives a transparent but distinct edge. Between pedestrian and auto paths they can be a safety barrier for the former. Put a line of trees one one lane into a street, as has been done on many European streets, to make a parking lane for example, and that lane becomes a part of the pedestrian realm while still functioning as a place to park cars. Even a few trees along the curb of a busy traffic street can have an impact if they are close enough together.

Which trees to use, their placement, their planting, and their maintenance are all important matters. Fortunately, studies abound on the physical nature, growing characteristics, and climatic and soil needs of individual trees. The best studies seem to be locally oriented. Continued observation of trees on the best streets allows for the strong conclusion that deciduous trees are more often appropriate than evergreens. Deciduous trees permit sunlight to reach the street in winter when it is either most needed or least a problem. Their leaf patterns are almost always dense than those of non deciduous trees and the leaves move more, subject to even slight wind changes; they permit light - mottled, moving light - to penetrate to the pedestrian, and this quality is characteristic of the best streets. Exceptions are easily found and enjoyed, the pines of teh Viale delle Terme di Caracalla, in Rome, and the palms of the Balm Beach Boulevard, in Palm Beach, Florida, for example, but overwhelmingly one finds deciduous trees on great streets.

To be effective, street trees need to be reasonably close together. If one objective is to create a line of columns that separate visually and psychologically one pathway from another, and if a further objective is to provide a canopy of branches and leaves to walk under, then the trees have to be planted close enough to do that. The close spacing may be more critical to creating a line that separates, because a canopy can often be achieved under a variety of spacings. Walking along a line of trees, it is desirable to be able to see between them, particularly between the first one or two, directly ahead, but also to be aware that one is indeed walking along a line, that the next tree and the following ones a distinct boundary, a plane. In practice, the most effective tree spacing is from 15 to 25 feet (4.5 to 7.6 meters) apart. On streets where the spacing reaches 30 feet (9 meters) or more, such as the Cours Mirabeau, in Aux-en-Provence, or Mills College, in Oakland, there are likely to be four rows of trees, or two a side. The trees along Monument Avenue, in Richmond, reach 36 feet apart but there are four rows. It is possible to find all kinds of reasons to plant them further that 25 feet apart - their health, a need to avoid having branches overlap, the required distances between light poles and even parking meters - but they don't seem to hold up in practice when spacing along the best streets is measured. Branches of trees along the Ramblas and Avenue Montiagne and the Ringstrasse, to name but three of many, overlap, and these trees have been around for a long time. The plane trees along Viale Manlio Gelsomini, in Rome, may be that street's only saving grace, and the spacing is often 15 to 18 feet. If there is a rule of thumb to be learned from the best streets, it would be that closer is better.

We come across other admonitions in regard to street trees, notably to avoid street corners by 40 or 50 feet (12 to 15 meters), for reasons o sight lines and therefore auto safety. Nonetheless, tree planting along the best streets either preceded or has otherwise managed to avoid such dictums; it comes as close as possible to street corners. In fact, one reason why street trees are often not effective is a combination of imposed spacing and corner distance rules. Assuming a 400-foot block (twice that of a north-south block in New York), a 50-foot corner distance requirements, and 50-foot spacing standard, there will be seven trees along a block and then 150-foor gap for the intersection; not very many trees. A 200-foot block would have only three trees.

The same spacing requirement help to explain why trees along center-of-street traffic medians are seldom effective. First there are the spacing requirements and then even greater distances required at intersections to allow for left turn lanes. The results are even fewer trees and larger gaps.

The spacing of trees along a street, once started, should not be stopped, not for driveways and not for buildings along the way. If the emphasis is to be on the design of the street as opposed to items along the way and if it is the street environment that is the object of design and building, then that end will not be achieved by responding to every "special circumstance". The argument usually involves not wanting trees to block the entrance to a major public or private building, or wanting to create a special place in front of a public building, or to omit a tree in favor of a bus stop or something similar. That doesn't work. It takes away from the street. There is a block along the Via Cola di Rienzo, in Rome, where trees have been omitted in front of a public market, and that block is nowhere near as pleasant an areas as the rest of the street. Along the Rablas, in Barcelona, trees have been omitted for a distance near the lower end, in front of the Theatre Principio, presumably to give presence to the theater, and there are elaborate five-luminaire streetlights instead. Trees would have been better, or both trees and lights.

Street trees, once established, are able to take considerable abuse. But on the best streets, where the trees make a major difference, they appear to be cares for. There seems to be, on those streets, a long-continuing program for maintenance, one based on an understanding of their importance. One assumes that they were planted well in the first place.

Street trees are a high-priority item on which to spend funds that could have a major environmental impact. Absent a commitment to do them right and to maintain them well later, the monies might as well not be spent. Done well and maintained well, street trees are grand.

Beginnings and Endings

Every street starts and ends somewhere and these locations are usually not too hard to fix. Perhaps in some preserve way it is the obviousness of the observation that keeps this form being an always present requirement for great streets. And yet, though the entry to Rosslyn Place is marked ever so subtly by two wrought iron gateposts, they are insignificant to that street's special character. It does not seem reasonable that every great street has to have something special, a physical thing, to mark its beginning or end, or that the start or finish should be crucial to making it what it is. Nonetheless, most great streets have notable starts and stops, not always fine, but notable. It could be argued that, since they have to start and stop somewhere, these points should be well designed.